Electrostatic printing apparatus of the offset type



June 11, 1968 DECKER ET AL 3,387,557

ELECTROSTATIC PRINTING APPARATUS OF THE OFFSET TYPE Filed Nov. 18, 1966 8 Sheets-Sheet l 147 7' W inf June 11, 1968 A. s. DECKER ET AL 3,387,557

ELECTROSTATIC PRINTING APPARATUS OF THE OFFSET TYPE Filed Nov. 18, 1966 8 Sheets-Sheet :3

BY wv/re Mai/VIN June 11, 1968 A. s. DECKER ET AL. 3,387,557

ELECTROSTATIC PRINTING APPARATUS OF THE OFFSET TYPE Filed Nov. 18, 1966 8 Sheets-Sheet 3 a 1. M Jam/ June 11, 1968 s, DECKER ET AL 3,387,557

ELECTROSTATIC PRINTING APPARATUS OF THE OFFSET TYPE Filed Nov. 18, 1966 8 Sheets-Sheet 4 47-7-0 (Mr/J June 11, 1968 s, DECKER ET AL 3,387,557

ELECTROSTATIC PRINTING APPARATUS OF THE OFFSET TYPE A E 5w SS 8 Sheets-Sheet 5 N\ lvll a? I J. M Q I h w L Q\\ aFQa-Di Ira/ear ZoTA FX/I Q. 1%.

Flled Nov 18 1966 June 11, 1968 A. s. DECKER ET Al. 3,387,557

ELECTROSTATIC PRINTING APPARATUS OF THE OFFSET TYPE Filed Nov. 18, 1966 8 Sheets-Sheet 6 X 72/67? mar/yd June 11, 1968 A. s. DECKER ET AL 3,387,557

ELECTROSTATIC PRINTING APPARATUS OF THE OFFSET TYPE Filed NOV. 18, 1966 8 Sheets-Sheet '7 5% w 9 f X 74 y! a 9 1,

$ A20 M W M0 74 l /011 I W 9 I20 5 /D4 A20 /Z 5 a 7/3 /04 5 I L 4 lf? +J i INVENTORS g H Max/4J4 14770 fir/FY June 11, 1968 A, s, DECKER ET AL 3,387,557

ELECTROSTATIC PRINTING APPARATUS OF THE OFFSET TYPE Filed NOV. 18, 1966 8 Sheets-Sheet 8 F/Z/M M/M 044%) United States Patent Office 3,387,557. Patented June 11, 1968 3,387,557 ELECTRGESTATIC PRINTING APPARATUS OF THE OFFSET TYPE Alfred S. Decker, Toledo, George R. Dhenshain, Syivania,

and Luther H. Wideman, Toledo, Ohio, assignors to Owens-Illinois, Inc, a corporation of flhio Filed Nov. 18, 1966, Ser. No. 595,499 6 Claims. ll. 10135) ABSTRAC'I OF THE DISCL'QPS Electrostatic printing apparatus of the offset type especially adapted for use in decorating articles having curved or irregular surfaces on a production line basis. A plurality of offset plate carriages are mounted upon an endless chain conveyor for movement with the chains and also for movement between a normal position and a projected position relative to the chains so that the offset printing element can be projected into operative relationship at both an image application station and an image transfer or decorating station. The carriage further includes means for resiliently bulging the offset printing element outwardly into conformed contact with an article surface during the decorating operation.

This invention relates to electrostatic printing apparatus of the offset type, and more particularly to electrostatic offset printing apparatus especially adapted for use in decorating articles having curved or irregular surfaces.

In the application of images by electrostatic offset techniques, the conventional method of applying the image to a curved article surface is to transfer the image from a flat offset element to the article surface by rotating the curved surface about its axis to roll the surface laterally across the flat offset element during the transfer of the image. For all practical purposes, this technique is restricted to singly curved surfaces, such as cylindrical or conical surfaces in which line contact or a constant spacirig can be maintained between the flat offset element and the article surface. Variations in spacing during the image transfer between the article and offset element surfaces result in non-uniform density in the applied image.

It is an object of the present invention to provide electrostatic offset printing apparatus in which an image of uniform density can be applied to article surfaces of doubly curved or irregular configuration.

It is another object of the invention to provide electrostatic oifset printing apparatus wherein a powder image may be applied to the offset element While the element is in a. fiat position and transferred from the offset element to the article while the offset element is accurately conformed to the precise shape of the surface to which the image is being transferred.

The foregoing, and other objects, are achieved in an electrostatic offset printing apparatus in which the offset element takes the form of a web of substantially inextensible sheet material which, in some instances may also be electrically conductive. The web-like offset element is mounted upon a carriage and is normally maintained in a flat stretched condition, as by tension springs connected to the periphery of the web. The offset element thus normally provides a fiat surface to which the image, in the form of an image-shaped layer of powder particles, may be applied conveniently.

The carriage is mounted upon a conveying means which conveys the carriage from an image application station at which the powder image is applied to a decorating station at which the image is electrostatically transferred from the offset element to the article surface. To conform the offset element to the shape of the surface to which the image is to be applied, the web-like offset element is bulged outwardly from its carriage into direct contact with the article surface during the image transfer operation. The bulging of the web-like offset element may be accomplished either by an inflatable element or by a resilient pad forced against the offset element to achieve the resilient bulged condition of the offset element during the decorating operation. The bulging of the offset element does not stretch the element, but instead forces the element outwardly from its carriage, this outward movement being resiliently resisted by the springs coupled to the periphery of the web-like offset element. When in the bulged condition, the offset element provides a resilient surface which, when forced into contact with the article surface, conforms itself to variations in the article surface automatically.

In those instances where the article decorated is a bottle, the normal technique of rolling the bottle laterally across the face of the offset element may be employed. In those cases where the surface to which the image is being applied is of relatively large radius, both the article and offset plate may be held stationary during the image application.

The offset element assembly is provided with means for establishing the electrostatic field to assist in the image transfer and, in those cases where the bulging means takes the form of an inflatable member, appropriate means are provided for inflating the inflatable member at the appropriate time.

Other objects and features of the invention will become apparent by reference to the following specification and to the drawings.

In the drawings:

FIGURE 1 is a side elevational view, partially in section, with certain parts omitted, one form of apparatus embodying the present invention;

FIGURE 2 is a top plan View, with certain parts omitted, of the structure of FIGURE 1;

FIGURE 3 is a detailed side elevational view, partially in section, showing the apparatus during the application of an image;

FIGURE 4 is a detailed top plan view, corresponding in general to FIGURE 3;

FIGURE 5 is a detail cross sectional view taken approximately on line 5--5 of FIGURE 4;

FIGURE 6 is a detail top plan view, partially in section, showing details of the offset plate carriage and inflating mechanism;

FIGURE 7 is a detail longitudinal cross sectional view of a. portion of the offset carriage and printing member;

FIGURE 8 is a cross sectional view taken on line 8-8 of FIGURE 7; and

FIGURE 9 is a detail cross sectional view taken on the line 99 of FIGURE 7;

FIGURE 10 is a partial top plan view of a modified form of the invention;

FIGURE 11 is a detail cross sectional view showing the plate assembly of FIGURE 10 in contact with the article during the decorating operation; and

FIGURE 12 is a detail cross sectional view showing a modification of the embodiment of FIGURES 10 and 11.

Referring first to FIGURES 1 and 2, one form of apparatus embodying the present invention includes generally an offset plate conveyor designated generally 20 and an article conveyor designated generally 22. In the particular apparatus shown, the articles being decorated take the form of bottles B having a doubly curved surface as at 24 to which a decorative image is to be applied. Bottle conveyor 22 has not been shown in detail, since its structure is conventional and Well known in the art. For the purposes of explanation of the present invention, conveyor 22 consists of a series of pairs of upper and lower bottle chucks 26 and 28 respectively, the chucks being carried on endless chains, not shown, for movement along an endless path, a portion of which is indicated by the broken line 30 of FIGURE 2. The upper and lower chucks are vertically aligned with each other and are supported upon their respective chains for free rotation about a vertical axis which is coincident with the vertical axis of a bottle B engaged by the chucks. Thus, bottle conveyor 22 is operable to convey bottles along the path 39, while at the same time permitting free rotation of the bottles about their vertical axis, as during the image transfer operation.

Ofiset plate conveyor 20 includes a pair of endless chains 32 operatively trained about end sprocket assemblies 34 and 36 for movement along, congruent paths lying in parallel planes. A series of offset plate carriage assemblies designated generally 38 are supported by and between chains 32 in a manner to be described in more detail below. End sprocket assembly 34 is intermittently driven by suitable drive means designated generally 49 in step-by-step movement, the length of each step of movement correr sponding to the distance between adjacent carriage assemblies 38. The path of movement of the carriage assemblies is in a clockwise direction as viewed in FIGURE 1 in which the carriage assemblies are located in registry with an image application station designated generally 42 at one point along their path and are subsequently carried to the image transfer station designated generally 44, at which the carriage is located in registry with a bottle B on bottle conveyor 22.

During the period of time in which a carriage 38 is located in operative registry with image application station 42, an image in the form of an image-shaped layer of printing powder particles is applied to the facing surface on carriage 38. Several methods of applying images are known in the art, see for example the pending application of James R. Profiitt, J12, Ser. No. 371,318 filed .iune 1, 1964, and assigned to the assignee of the present application. The printing powder particles employed in the process under discussion are capable of being electrically charged, and electrostatic transfer techniques are employed both in applying the image to the offset plate and to the subsequent transfer of the powder image from the plate to the surface of the article.

Details of carriage assemblies 38 are best shown in FIG- URES 6-9 of the drawings.

Referring first to FIGURE 6, each assembly 38 includes a carriage frame 46 which is suspended between chains 32 by brackets 48 which are fixedly secured to frame 46 and coupled to a link of each of chains 32. Frame 46 is formed With a pair of cylindrical bushing bosses 50 having internal bores 5'2 which slidably receive a pair of support rods 54 fixedly secured at their forward ends to a cross piece 56 which forms a part of the offset plate holder assembly 57. The rearward ends of support rods 54 are coupled to each other by a bracket assembly 58 formed with a pair of cylindrical recesses 60 which surround the rearward ends of rods 54 in spaced relationship to define pockets within which compression springs 62 are seated. Compression springs 62 act between the rearward end of bushing bosses 50 of carriage frame 46 and member 58 to resiliently bias support rods 54 and cross member 56 rearwardly with respect to frame 46 to the normally maintained conveying position shown in FIGURE 6.

At the central portion of member 58, a bracket-like element 64 is formed to rotatably support a cam follower roller 66 which may be engaged by a cam 68 mounted for sliding movement upon the shaft 70 of sprocket assembly 36. Upon rocking rotation of shaft 188, cam 68 engages follower roller 66 (by means described hereinafter in detail) to force support rods 54 and cross member 56 for- Wardly from the FIGURE 6 position. This action carries the offset plate assembly outwardly to its operative positon shown in FIGURES 4 and 5.

The offset plate assembly is supported from cross memher 56 by a pair of forwardly projecting members 72 constructed of electrical insulating material.

Referring now to FIGURES 79, details of the offset plate assembly are shown. The assembly includes a base plate 74 of generally rectangular configuration which is fixedly mounted upon the forward ends of members 72 as by mounting blocks 76. The forward face of plate 74 is covered completely by one side of a tubular rubber gasket 78 which provides a means for sealing a recessed plate 80 to the front surface of plate 74. Recessed plate 3% is inserted in tubular gasket 78 and fixedly secured to plate 74 as by mounting bolts 82 to define a recess 84 at the front side of plate '74. Recessed plate 80 is bored at several locations as at 86, and a relatively large tube 33 passes through plate 74 to project through element 78 into the interior of chamber 84.

As best seen in the cross sectional view of FIGURE 9, gasket 73 snugly surrounds recessed plate 80 and opposite or open ends of the tubular gasket are sealed shut by clamp assemblies 96 which are fixedly bolted to plate 74 as by bolts 92. Thus, the tubular gasket 78 defines a closed chamber which normally communicates with the atmosphere via tube 88. A pair of relatively short tubular members 94 are fixedly mounted along the shorter sides of plate 74 by adapter elements 96 of electrical insulating material. Similar, but longer thicker tubular elements 98 are likewise mounted along the longer sides of rectangular plate 74 by means of adapter elements 106 which are likewise formed of electrical insulating material.

Tubular members 9-.- and 93 form a rounded peripheral surface about which a flexible and substantially inextensibie printing element 102 of sheet material is supported, the web of sheet material 162 completely overlying the front (upper in FIGURE 7) surface of the offset plate assembly. The sheet 192 is of generally rectangular configuration with the corners cut away so that, when mounted upon tubular members 94 and 98, the sides of the sheet correspond to the respective lengths of the tubular members about which they are trained. To the shorter side edges 104 are attached plate-like extension elements 186 and 1% respectively. Element 106 is formed with an opening 110 to provide clearance for one f support posts 72, while element 198 is somewhat longer than element 166 and is formed with a more elongate opening 112 to provide clearance for the other post 72 and for tube 88. Elements 106 and 108 are connected to each other by a series of tension springs 114 which apply tension to Web element 102 to stretch the web longitudinally. The longer edges 116 of web element 102 are fixedly secured to elongate plates 118 which are likewise resiliently coupled to each other by a series of tension springs 120 to apply tension to web element 102 tensioning the web transversely. It will be noted that tubular members 98 are of a larger diameter than are tubular members 94 and that the forward surfaces of both members 9 and 93 lie in the same general plane. The larger diameter of members 98 provides a clearance so that transverse tensioning springs 120 can pass freely clear of tensioning springs 114 and plates 106 and 108, as best seen in FIGURES 7 and 9.

While web member itself is inextensible, the resilient tensioning of the web member permits the web member to be expanded outwardly from the front of the plate assembly when air under pressure is supplied to chamber 84- and passes through passages 86 to inflate the closed tubular gasket 78. Springs 114 and 120 can stretch to accommodate separation of the opposed edges of web 102 as required by the inflation of the tubular gasket, and the smoothly curved surfaces of tubular members 94 and 98 permit the smooth sliding of the material of web 102 around the surfaces.

Referring now to FIGURE 6, it is seen that tube 88 is connected to second tubular member 120A which is fixedly mounted upon a mounting post 122 attached in turn to carriage frame 46. Member IZtlA is formed with an internal passage 124 which communicates with the passage in the interior of tube 88. Because the support plate assembly is mounted for movement relative to carriage frame 46, tube 88 is flexible and, by flexing can accommodate the relative movement between the support plate assembly and tubular member 120A.

Air for inflating tubular gasket 78 is supplied, when the assembly is in the image transfer position, by a valve assembly 126 which is operable to connect a source of air under pressure P to passage 124. Valve 126 includes a housing 128 having a first bore 130 within which a valve stem 132 is slidably mounted. An inlet fitting 134 places air source P in communication with a relatively short enlarged diameter section 136 of passage 130. Air under pressure is normally confined within enlarged diameter section 136 by the close fit of stem 132 within bore 138. A reduced diameter section 138 on stem 132 is formed with a radial bore 140 which communicates with a central passage 142 which extends along the axis of valve stem 132 from bore 140 to the right-hand end of the valve stem as viewed in FIGURE 6.

Reduced diameter section 138 is normally maintained in the FIGURE 6 position by a compression spring 144 mounted in a second enlarged bore 146 in housing 128. Spring 144 is seated between the shoulder formed at the right-hand end of section 146 and a piston head 148 slidably received within bore 146. A fitting 158 having an internal passage 152 closes the left-hand end of bore 146 and places the chamber between the left-hand side of piston 148 and fitting 150 in communication with an inlet conduit 154. When pressure is supplied to conduit 154, piston 148 and valve stem 132 are driven to the right as viewed in FIGURE 6 until reduced diameter section 138 is in alignment with enlarged diameter portion 136. This action places pressure source P in communication with bore 140, and passage 142 and at the same time, a sealing lip 156 is driven into sealing engagement with the end of tubular member 120A thereby placing passage 124 and tube 88 in communication with pressure source P.

Valve assembly 126 is mounted upon a bracket 156 which is in turn mounted upon the fixed frame of plate conveyor 20.

An electric contact assembly 160 is mounted upon frame member 46 to electrically charge the plate assembly. An electric cable 162 electrically connects the contactor of contact 160 to plate 74 and mounting bolts 82 electrically connect recessed plate 80 to plate 74 through one wall of tubular gasket 78. Contact assembly 160 includes a spring loaded contactor 164 which, when the plate assembly is in the image transfer position, will contact a stationary electric contact 166 (FIGURE 6) mounted upon a stationary member 168 of the plate conveyor frame. The electrical circuit is, of course, electrically insulated from the conveyor and carriage frames. Contact 166 is connected to a suitable source of electric potential, not shown, by an electric lead 170.

Referring briefly to FIGURE 6, the offset plate assembly is normally disposed in what may be termed a retracted position upon carrier frame 46 by the action of compression springs 62, the offset plate assembly being shown in its normal retracted position in FIGURE 6. When in this position, and with the offset plate assembly in its uninflated position, the forward surface of web 182 is retracted clear of the path of movements of bottles B on the bottle conveyor. During the application of an image to the bottle surface the offset plate assembly is inflated and, at the same time projected outwardly into the position shown in FIGURES 3, 4 and 5 so that a firm pneumatically cushioned contact is achieved between the surface of web 102 and the bottle during the image transfer operation. This action is especially important where, as in the illustrated case, the surface being printed is curved. The structure for projecting the offset plate assembly by actuation of cam 68 is most clearly shown in FIGURES 3, 4 and 5.

Referring first to FIGURES 4 and 5, a stationary frame member 172 is fixedly mounted upon the frame of plate conveyor 20 and has a central offset portion 174 which extends transversely across the conveyor closely behind the shaft 78 of sprocket assembly 36. The offset shape of frame members 172 is solely for the purpose of providing clearance for the sprockets 36 while locating the central portion closely adjacent the sprocket shaft. A bracket member 176 is fixedly mounted upon central portion 174 and is formed with elongate guide slots in its upper and lower surfaces which slidably receive and guide a rearward extension 180 of cam member 68. At the rearward end of extension 180, a pair of projecting ears 182 serve to rotatably support a follower roller 184. A compression spring 186 is seated between bracket 176 and rearward extension 180 to resiliently bias the extension and its integral cam portion 68 tothe left as viewed in FIGURES 3 through 5.

At a location behind frame member 172, a rockshaft 188 is journalled in the frame of plate conveyor 20 for rotary oscillation and carries a cam 190 fixedly mounted upon the rockshaft. Rockshaft 188 also has a cam surface 192 operable when cam 190 is in the full line position of FIGURE 5 to engage roller 184 to force extension 180 and its cam 68 to the right as viewed in FIGURES 3 through 5. This causes cam 68 to engage follower roller 66 on the movable portion of carriage 38 to thereby force the offset plate assembly outwardly to the right into firm engagement with the bottle. Upon rotary oscillation of carn 190 to the dotted line position shown in FIGURE 5, the small radius portion of cam 192 is engaged with follower roller 184, thereby permitting cam 68 to move to the left to the broken line position of FIGURE 5, under the influence of compression spring 186, thereby permitting cam 68 and the support plate assembly to likewise shift back to the left.

In the absence of any rotary force applied to shaft 188, cam 190 will assume the broken line position of FIGURE 5. Cam 198 is driven in rotary oscillation to the FIGURE 5 position by a second cam assembly which includes a crank 194 fixed to an extension of rockshaft 188 and having a follower roller 196 engaged with the peripheral surface of still another cam- 198 rotatably mounted upon a shaft 288 journalled in the frame of plate conveyor 20. Shaft 208 is driven in rotation as by a chain and sprocket assembly 202 which is in turn driven through appropriate mechanism from plate conveyor drive 40. Cam 198 has an enlarged radius portion 204 which, when engaged with follower roller 196 of crank 194 holds the crank in the elevated position shown in FIGURE 3 which in turn corresponds to the elevated position of earn 190 in FIGURE 5.

OPERATION OF THE EMBODIMENT OF FIGURES 1 THROUGH 9 In operation, plate conveyor 20, as described above is driven in intermittent step-by-step movement, each step corresponding to the distance or spacing between adjacent carriers 38 upon chains 32. The time period of delay between successive steps of movement of conveyor 20 is synchronized with the rate of movement of bottles B on bottle conveyor 22, which is driven to move the bottles in continuous movement at a constant rate of speed along path 30. The time period of delay between successive steps is long enough so that upon arrival of a carrier 38 at image application station 44, the offset plate source P to inlet conduit d of valve 126, thereby supplying air under pressure to the left-hand side of piston 148. This causes the piston and valve stem to drive to the right as viewed in FIGURE 6, thereby establishing a connection between passage 142 of valve 126 and conduit 120A of the plate assembly. When this contact is made,

the reduced diameter section 138 on the valve stem is in registry with the enlarged diameter section of the bore in the valve body, thereby placing inlet conduit 13d and pressure source P in communication with passage 142 Via passage 140 to conduit air under pressure to the plate assembly to inflate the plate assembly.

This connection is maintained throughout the image transfer operation. The time period during which the plate assembly is maintained inflated is determined by the angular extent of the enlarged diameter portion 212 on cam 206 which maintains switch 2% closed for the desired interval. When rotation of shaft 2% carries the enlarged diameter portion 212 beyond switch 2%, the switch opens, releasing the solenoid of valve 218 which then shifts to close the valve connection to pressure source P and at the f same time to vent conduit 154. Venting of conduit 154 permits piston 148 to be restored to the FIGURE 6 position by spring 144, thereby blocking communication between valve inlet 134 and passage 142, and at the same time retracting the valve stem from its sealed engagement with conduit 120A of the plate assembly to vent and thereby deflate the plate assembly.

The offset plate assembly is held extended and inflated as the bottle is conveyed past web 102, the bottle contacting and depressing the inflated assembly as shown in FIGURE 4 so that full and complete contact of the powder image on web 102 and the bottle surface occurs. The frictional engagement and pressure causes the bottle to rotate and roll with no-slip contact across web 102 as the bottle is conveyed past the offset plate assembly by bottle conveyor 22. Thus, the powder image is held effectively stationary and the bottle surface is rolled across the image. Because of the fact that Web m2 is substantially inextensible, little, if any stretching or smearing of the powder image is occasioned during the transfer. The transfer is a In FIGURES 10 and 11 there is shown a modified form of plate assembly 38' which will be used in the same environment as the previously described embodiment of FIGURES 1 through 9. The plate assembly 38' differs from that of FIGURES 1 through 9 in that the mechanism for shifting the plate assembly from its normal position relative to chains 32' to its operative position is mounted adjacent the image transfer station rather than upon the carriage itself as in the previously described embodiment. Reference numerals with primes applied in FIGURES 10 and 11 indicate corresponding structure identified by unprimed numerals in FIGURES 1 through 9.

Plate assembly 38' includes a flexible inextensible web 220 of electrically conductive material, such as silicon rubber which is suspended within a frame 222 as by a series of tension springs 224 which maintain web 222 taut and under tension, and further serve as an electrical connection between web 220 and frame 222. Frame 222 is mounted upon chains 32' by brackets 226.

In the embodiment of FIGURES 10 and 11, the cylindrical bushing bosses 5d are not mounted upon the carriage, but instead are fixedly mounted upon the frame of the bottle conveyor. As in the previous embodiment, support rods 54' are slidably mounted within bushing bosses 5G and support an inflation assembly designated generally 2128. Assembly 228 includes a recessed back plate 239 having a rubber diaphragm 232 sealingly clamped to its periphery by a peripheral clamp frame 234. The diaphragm and the recess in plate 230 cooperate to define a closed chamber which communicates with a source of air under pressure via a solenoid controlled valve 210'.

An electrical contactor is mounted upon frame 222 to engage a contact 166 when carriage 38' is at the image transfer station. Operation of the embodiment of FIGURES l0 and 11 differs from that of the previously described embodiment only by virtue of the structural differences described above. The inflation assembly 228 is reciprocated between its normal and extended positions by actuation of member 68 which is actuated by the same structure as described previously in connection with the embodiments of FIGURES 1 through 9. Valve 210' is actuated in the same manner as valve 210 of the FIG- URES 1 through 9 embodiment.

In FIGURE 12, there is shown a further embodiment of the present invention which may best be described as a modification of the embodiment of FIGURES 10 and 11. In the embodiment of FIGURE 12, inflation assembly 228 of FIGURES l0 and 11 has been modified by replacing the inflatable portion of assembly 228 with a resilient element 240 of urethane foam or the like which is shaped to conform, in general to the inflated condition of inflation assembly 228 of FIGURES l0 and 11. Like inflation assembly 228 of FIGURES l0 and 11, the resilient pad assembly 228' of FIGURE 12 is mounted upon the frame of the bottle conveyor adjacent the decorating station and is driven into and out of engagement with a web element as in the case of FIGURES 10 and 11.

While various embodiments of the invention have been described, it will be apparent to those skilled in the art that the described embodiments may be modified. Therefore, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is that defined in the following claims.

We claim:

1. In an electrostatic offset printing apparatus for decorating an article surface, said apparatus having first conveying means for conveying an article to be decorated to a decorating station, offset printing means, second conveying means for conveying said offset printing means to an image application station and thence to said decorating station, means at said image application station for applying an image shaped layer of powder particles to said offset printing means, and means operable when said offset printing means and an article are at said decorating station for electrostatically transferring said layer of powder particles from said offset printing means to said article surface; the improvement wherein said second conveying means comprises a pair of spaced parallel endless chains, said offset printing means comprising a plurality of carriage support means mounted at spaced locations upon and extending transversely between said endless chains for movement therewith, a carriage mounted upon each of said carriage support means for movement between a normally maintained conveying position and an operative position wherein said carriage is projected outwardly from said chains, a flexible web-like offset element of substantially inextensible sheet material resiliently mounted upon said carriage in a flat stretched condition and adapted to receive said image shaped layer of printing powder particles at said image application station while in said flat stretched condition, first means operable when a carriage is located at said decorating station for shifting said carriage from said normal position to said operative position and resiliently bulging said offset element outwardly from said carriage into contact with the surface of an article located at said decorating station to cause said olfset element to resiliently conform to the article surface, and second means operable to establish an electrical field to transfer printing powder particles from said ofiset element to said article surface while said offset element is in conformed contact with said article surface.

2. An electrostatic oifset printing apparatus as defined in claim 1 wherein said first means operable comprises a resilient pad movably mounted upon said second conveying means adjacent said decorating station, and means operable when said carriage is located at said decorating station for moving said pad against said offset printing element to bulge said offset element outwardly from said carriage into contact with the surface of said article.

3. An electrostatic offset printing apparatus as defined in claim 1 wherein said otfset element is of electrically conductive material.

4. In an electrostatic offset printing apparatus as defined in claim 1; the further improvement wherein said first means operable comprises inflatable means operable to resiliently bulge said offset element outwardly from said carriage.

5. In an electrostatic ofiset printing apparatus as defined in claim 4, the further improvement wherein said inflatable means is mounted upon said carriage, and means operable 10 when said carriage is located at said decorating station for inflating said inflatable means.

6. In an electrostatic offset printing apparatus as defined in claim 5; the further improvement wherein said means for inflating said inflatable means comprises a movable valve member mounted upon said second conveying means adjacent said decorating station, means defining an inlet conduit on said carriage, and means operable upon location of said carriage at said decorating station for connecting said valve means to said inlet conduit.

References Cited UNITED STATES PATENTS 2,016,450 10/1935 Myers 10l35 2,077,790 4/1937 Hakogi 101 35 2,124,711 7/1938 Rowell 101-211 X 2,184,510 12/1939 Adams 10l35 X 2,484,671 10/1949 Bauman.

2,745,339 5/1956 Fernandez 101-129 X 2,904,916 9/1959 Stahmann 10135 3,276,358 10/1966 Lusher 101129 ROBERT E. PULFREY, Primary Examiner.

E. S. BURR, Assistant Examiner. 

